Loads content and renders it inside the panel.

<div class="definition">
    load(panel, url, [transition])
</div>

<div class="arguments">
    <table>
    <tr>
        <td>panel</td>
        <td><b>string</b>, name of the panel</td>
    </tr>
    <tr>
        <td>url</td>
        <td><b>string</b>, server url to load content from</td>
    </tr>
    <tr>
        <td>transition</td>
        <td><b>string</b>, name of the transition (<i>optional</i>)</td>
    </tr>
    </table>
</div>

Returns <i>promise</i> that is resolved when content is loaded.

<h4>Description</h4>

This method loads content for the panel from the <span class="argument">url</span>. The content should be Text or HTML and should not include JavaScript. The first argument <span class="argument">panel</span> is the name of the panel. It can be one of the following:
<ul style="margin-left: 50px">
    <li>top
    <li>left
    <li>main
    <li>right
    <li>preview
    <li>bottom
</ul>
The second argument <span class="argument">url</span> is the location to load content from.
You can optionally provide <span class="argument">transition</span> that defines visual transition to the new content.
The transition is done using <a href="w2utils.transition">w2utils.transition()</a> method and it can be one of the following:
<ul style="margin-left: 50px">
    <li>slide-left
    <li>slide-right
    <li>slide-up
    <li>slide-down
    <li>flip-left
    <li>flip-right
    <li>flip-up
    <li>flip-down
    <li>pop-in
    <li>pop-out
</ul>

Below is an example  how to set content to the layout panel:
<textarea class="javascript">
let layout = new w2layout({
    name: 'layout',
    panels: [
        { type: 'top', size: 40 },
        { type: 'main', html: 'This is main panel' },
        { type: 'preview', size: 200 }
    ]
});

// return current content
w2ui.layout.load('main', 'http://domain.com/path/to/file', 'slide-left')
    .then(() => { console.log('Content is loaded')})
</textarea>
